Neutralizing layers in diffusion transfer photographic film

ABSTRACT

Photographic systems employing an acid neutralizing layer comprising a polymeric salt of a monomeric strong acid and a polymeric weak base, i.e., polymeric salts which hydrolyze to give an acid reaction.

United States Patent mi Taylor 1 1 Aug. 28, 1973 NEUTRALIZING LAYERS IN DIFFUSION [56] References Cited TRANSFER PHOTOGRAPHIC FILM UNITED STATES PATENTS [75] Inventor: Lloyd D. Taylor, Lexington, Mass. 3,415,646 12/1968 Land 96/3 [73] Assrgnee: lri'gasisoid Corporation, Cambridge, Primary Examinepd. Travis Brown Assistant Examiner-Richard I... Schilling [22] Filed: Dec. 16, 1971 Attorney-Alvin Isaacs et al.

pp 57 ABSTRACT Photographic systems employing an acid neutralizing C(i1 96/3, 96/29G layer comprising a polymeric Salt of a monomeric 58] Fieid 76 C 77 strong acid and a polymeric weak base, i.e., polymeric 5 salts which hydrolyze to give an acid reaction. 23 Claims, 1 Drawing Figure 127* A SUPPORT 3r\\ CYAN DYE DEVELOPER LAYER by RED-SENSITIVE SILVER HALIDE EMULSION LAYER v lNTERLAYER MAGENTA DYE IIVELOPER LAYER GREEN-SENSlTlVE SILVER HALIDE EMULSION LAYER /+/-INTERLAYER YELLOW DYE DEVELOPER LAYER BLUE-SENSITIVE SILVER HALIDE EMULSION LAYER /-AUX|LlARY LAYER lMAGE- RECElVlNG LAYER l SPACER LAYER l i I -NEUTRAL1ZING LAYER SUPPORT PAIENIED M1928 ms SU PPORT CYAN DYE DEVELOPER LAYER |NTERLAYER /\MAGENTA DYE DEVELOPER LAYER GREEN-SENSITIVE SILVER HALIDE EMULSION LAYER I- -INTER LAYER -YELLOW DYE DEVELOPER LAYER BLUE-SENSITIVE SILVER HALIDE EMULSION LAYER /AUXILIARY LAYER IMAGE-RECEIVING LAYER L SPACER LAYER iNEUTRALlZlNG LAYER SUPPORT INVENT LLOYD DJAY NEYS . 1 t NEUTRALIZING LAYERS IN DIFFUSION TRANSFER PHOTOGRAPH-[1C FILM BACKGROUND OF THE INVENTION Various diffusion transfer systemsfor forming color images have heretofore been disclosed in the art. Generally speaking, such systems rely for color image formation upon a differential in mobility or solubility of a dye image-providing material obtained as a function of development so as to provide an imagewise distribution of such material which is more diffusible and which is therefore selectively transferred, at least in part, by diffusion, to a superposed dyeable stratum to impart thereto the desired color transfer image. The differential in mobility or solubility may'for example be obtained by a chemical action such as a redox reaction or a coupling reaction.

The dye image-providing materials which may be employed in such processes generally may be characterized as either (I) initially soluble or diffusible in the processing composition but are selectively rendered non-diffusible in an imagewise pattern as a function of development; or (2) initially insoluble or non-diffusibl'e in the processing composition but which are selectively rendered diffusible in an imagewise pattern as a function of development. These materials may be complete dyes or dye intermediates, e.g., color couplers.

As examples of initially soluble or diffusible materials and their application in color diffusion transfer, mention may be made of those disclosed, for example, in US. Pat. Nos. 3,647,049; 2,661,293; 2,698,244; 2,698,798; 2,802,735; 2,744,668; and 2,983,606. As examples of initially non-diffusible materials and their use in color transfer systems, mention may be made of the materials and systems disclosed in U. S. Pat. Nos. 3,443,939; 3,443,940; 3,227,550; 3,227,551, 3,227,552; 3,227,554; 3,243,294 and 3,445,228.

In any of these systems, multicolor images are obtained by employing a film unit containing at least two selectively sensitized silver halide layers each having associated therewith a dye image-providing material exhibiting desired spectral absorption characteristics. The most commonly employed elements of this type are the so-called tripack structures employing a blue-, a greenand a red-sensitive silver halide layer having associated therewith, respectively, a yellow, a magenta and a cyan dye image-providing material.

A particularly useful system for forming color images by diffusion transfer is that described in U. S. Pat. No. 2,983,606, employing dye developers (dyes which are also silver halide developing agents) as the dye imageproviding materials. In such systems, a photosensitive element comprising at least one silver halide layer having a dye developer associated therewith (in the same or in an adjacent layer) is developed by applying an aqueous alkaline processing composition. Exposed and developable silver halide is developed by the dye developer which in turn becomes oxidized to provide an oxidation product which is appreciably less diffusible than the unreacted dye developer, thereby providing an imagewise distribution of diffusible dye developer in terms of unexposed areas of the silver halide layer, which imagewise distribution is then transferred, at least in part, by diffusion, to a dyeable stratum to impart thereto a positive dye transfer image. Multicolor images may be obtained with a photosensitive element having two or more selectively sensitized silver halide layers and associated dye developers, a tripack structure of the type described above and in various patents including the aforementioned U. S. Pat. No. 2,983,606 being especially suitable for accurate color recordation of the original subject matter.

In color diffusion transfer systems of the foregoing description, color images are obtained by exposing a photosensitive element or negative component" comprising at least a light-sensitive layer, e.g., a gelatino silver halide emulsion layer, having a dye imageproviding material associated therewith in the same or in an adjacent layer, to form a developable image; developing this exposed element with a processing composition to form an imagewise distribution of a soluble and diffusible image-providing material; and transferring this imagewise distribution, at least in part, by diffusion, to a superposed receiving elementor positive component comprising at least a dyeable stratum to impart to this stratum a color transfer image. The negative and positive components may be separate elements which are brought together during processing and thereafter either retained together as the final print or separated following image formation; or they may together comprise a unitary structure, e.g., integral negative-positive film units wherein the negative and positive components are laminated and/or otherwise physically retained together at least prior to image formation.

While the present invention is applicable both to those systems wherein the dyeable stratum is contained on a separate element and to those systems wherein the dyeable stratum and the photosensitive strata comprise a unitary structure, of particular interest are those integral negative-positive film units adapted for forming color transfer images viewable without separation, i.e., wherein the positive component need not be separated from the negative component for viewing purposes. Generally, such film units comprise a plurality of essential layers including a negative component comprising at least one light-sensitive silver halide and associated dye image-providing material and a positive component comprising dyeable stratum. These components may be laminated together or otherwise secured together in physical juxtaposition as a single structure. Film units intended to provide multicolor images comprise two or more selectively sensitized silver halide layers each having associated therewith an appropriate dye image-providing material exhibiting desired spectral absorption characteristics. As was heretofore mentioned the most commonly employed negative components for forming multicolor images are of the tripack structure containing a blue-, a greenand aredsensitive silver halide layer having associated therewith in the same or in a contiguous layer a yellow, a magenta and a cyan dye image-providing material respectively. lnterlayers or spacer layers may if desired be provided between the respective silver halide layers and associated dye image-providing materials. In addition to the aforementioned essential layers, such film units further include means for providing a reflecting layer between ing layer may comprise a preformed layer of a reflecting agent included in the essential layers of the film unit or the reflecting agent may be provided after photoexposure, e.g., by including the reflecting agent in the processing composition. These essential layers are preferably contained on a transparent dimensionally stable layer or support member positioned closest to the dyeable stratum so that the resulting transfer image is viewable through this transparent layer. Most preferably another dimensionally stable layer which may be transparent or opaque is positioned on the opposed surface of the essential layers so that the aforementioned essential layers are sandwiched or confined between a pair of dimensionally stable layers or support members, at least one of each is transparent to permit viewing therethrough of a color transfer image obtained as a function of development of the exposed film unit in accordance with the known color diffusion transfer system such as will be detailed hereinafter. In a particularly preferred form such film units are employed in conjunction with a rupturable container of known description containing the requisite processing composition and adapted upon application of pressure of applying its contents to develop the exposed film unit, e.g., by applying the processing composition in a substantially uniform layer between the dyeable stratum and the negative component. It will be appreciated that the film unit may optionally contain other layers performing specific desired functions, e.g., spacer layers, etc.

Opacifying means may be provided on either side of the negative component so that the film unit may be processed in the light to provide the desired color transfer image. In a particularly useful embodiment such opacifying means comprise an opaque dimensionally stable layer or support member positioned on the free'or outer surface of the negative component, i.e., on-the surface of the film unit opposed from the positive component containing the dyeable stratum to prevent photoexposure by actinic light incident thereon from this side of the film unit and an opacifying agent applied during development between the dyeable stratum and the negative component, e.g., by including the opacifying agent in a development composition so applied, in order to prevent further exposure (fogging) by actinic light incident thereon from the other side of the film unit when the thus exposed film unit is developed in the light. The last-mentioned opacifying agent may comprise the aforementioned reflecting agent which masks the negative component and provides the requisite background for viewing the transfer image formed thereover. Where this reflecting agent does not by itself provide the requisite opacity it may be employed in combination with an additional opacifying agent in order to prevent further exposure of the light-sensitive silver halide layer or layers by actinic light incident thereon.

As examples of such integral negative-positive film units for preparing color transfer images viewable without separation as reflection prints, mention; may be made of those described and claimed in U. S. Pat. Nos. 3,415,644; 3,415,645; 3,415,646; 3,473,925; 3,573,043; 3,576,625; 3,573,042; 3,594,164; and 3,594,165.

In general, the integral negative-positive film units of the foregoing description, e.g., those described in the aforementioned patents, are exposed to form a developable image and thereafter developed by applying the appropriate processing composition to develop exposed silver halide and to form, as a function of development, an imagewise distribution of diffusible dye image-providing material which is transferred, at least in part by diffusion, to the dyeable stratum to impart thereto the desired color transfer image, e.g., a positive color transfer image. Common to all of these systems is the provision of a reflecting layer between the dyeable stratum and the photosensitive strata to mask effectively the latter and to provide a background for viewing the color image contained in the dyeable stratum, whereby this image is viewable without separation, from the other layers or elements of the film unit. In certain of these systems, this reflecting layer is provided prior to photoexposure, e. g., as a preformed layer included in the essential layers of the laminar structure comprising the film unit, and in others it is provided at some time thereafter, e. g., by including a suitable lightreflecting agent, for example, a white pigment such as titanium dioxide, in the processing composition which is applied between the dyeable stratum and the next adjacent layer to develop the latent image and to form the color transfer image.

The dye image-providing materials which may be employed in such processes generally are selected from those materials heretofore mentioned and disclosed in the illustra-tive patents which were initially soluble or diffusible in the processing composition but which are selectively rendered non-diffusible as a function of development or those which are initially insoluble or nondiffusible in the processing composition but are selectively rendered diffusible as a function of development. These materials may be complete dyes or dye intermediates, e. g., color couplers.

A preferred opacification system to be contained in the processing composition is that described in the copending applications of Edwin H. Land, SOr. No. 43,782, filed June 5, 1970 (now abandoned) and S0r. No. 101,968, filed Dec. 28, 1970, now U.S. Pat. No. 3,647,437, comprising an inorganic reflecting pigment dispersion containing at least one optical filter agent at a pH above the pKa of the optical filter agent in a concentration effective, when the processing composition is applied, to provide a layer exhibiting optical transmission density than about 6.0 density units with respect to incident radia-tion actinic to the photosensitive silver halide layer and optical reflection density than about 1.0 density with respect to incident visible radiation.

In lieu of having the reflecting pigment contained in the processing composition, e.g., as disclosed in the aforementioned copending applications, the reflecting pigment needed to mask the photosensitive strata and to provide the requisite background for viewing the color transfer image formed in the receiving layer may be contained initially in whole or in part as a preformed layer in the film unit. As an example of such a preformed layer, mention may be made of that disclosed on the copending applications of Edwin H. Land, Ser.

Nos. 846,441, filed July 31, 1969, and 3,645, filed Jan. 19, 1970 now U.S. Pat. Nos. 3,615,421 and 3,620,724, respectively. The reflecting pigment may be generated in situ as is disclosed in the copending applications of Edwin H. Land, Ser. Nos. 43,741 and 43,742, both filed June 5, 1970, now U. S. Pat. Nos. 3,647,434 and 3,647,435, respectively.

In the various color diffusion transfer systems which have previously been described and which employ an aqueous alkaline processing fluid, it is well known to employ an acid-containing layer to lower the environmental pl-I following substantial dye transfer in order to increase the image stability and/or to adjust the pH from a first pH at which the imaging dyes are diffusible to a second (lower) pH at which they are not. For example, U. S. Pat. No. 3,362,819 discloses systems wherein the desired pl-l reduction may be effected by providing a polymeric acid layer adjacent the dyeable stratum. These polymeric acids may be polymers which contain acid groups, e.g., carboxylic acid and sulfonic acid groups, which are capable of forming salts with alkali metals or with organic bases; or potentially acidyielding groups such as anhydrides or lactones. Preferably the acid polymer contains free carboxyl groups. An inert interlayer or spacer layer may be disposed between the polymeric acid layer and the dyeable stratum in order to control the pH reduction so that it is not premature and hence interferes with the development process, e.g., the time" control the pH reduction. Suitable spacer or timer" layers for this purpose are described with particularity in this patent and in others, including U. S. Pat. Nos. 3,419,389; 3,421,893; 3,433,633; 3,455,686; and 3,575,701.

The copending application of Schlein et al., Ser. No. 165,171, filed July 22, 1971, describes and claims an acid layer comprising a water-soluble acid and a watersoluble binder in film units such as those previously described and including a negative component comprising at least one light-sensitive silver halide layer and an associated dye image-providing material and a positive component containing a dyeable stratum. As is disclosed in this copending application, the use of such water-soluble ingredients in the neutralizing layer affords many distinct advantages over systems employing water-insoluble components which need be coated from an organic solvent. Apart from the readily apparent coating advantages in avoiding the use of organic solvents, is that it permits the use of shorter acid molecules with lower equivalent weights, which in turn permits one to employ thinner coatings, an important advantage in the film units to which the copending application is directed.

While the acid layer is preferably contained in the receiving element employed in systems wherein the dyeable stratum and photosensitive strata are contained on separate-elements, e.g., between the support for the receiving element and the dyeable stratum; or associated with the dyeable stratum in those integral film units, e.g., on the side of the dyeable stratum opposed from the negative component, the acid layer may, if desired, be disposed in a layer associated with the photosensitive strata, as is disclosed, for example, in U. S. Pat. Nos. 3,362,821 and 3,573,043.

U. S. Pat. No. 3,576,625 discloses integral film units containing yet another neutralizing system for lowering the pH. In accordance with that disclosure, the film unit is constructed to contain at least one layer containing a particulate dispersion of acid material. In general, this acid material may comprise any photographically nondeleterious acid material in solid or liquid state encapsulated within a polymeric wall material which is permeable to the alkaline processing composition.

The present invention is directed to another type of neutralizing material for lowering the environmental pH in color diffusion transfer systems of the type previously described, which material provides the distinct advantages and beneficial results which will be described hereinafter in the detailed description of the invention.

BRIEF DESCRIPTION OF DRAWING The FIG. is an enlarged, fragmentary, diagrammatic. sectional view of a film unit contemplated by this invention.

SUMMARY OF THE INVENTION In accordance with the present invention a layer comprising a polymeric salt of a strong acid and a weak base is employed to lower the pH. This salt hydrolyzes to give an acid reaction and as a function thereof and the subsequent lowering of the pH forms a polymeric base, as distinguished from neutralization reactions wherein an acid reacts with a base to form a salt. [This reaction will be explained in more detail hereinafter.]

DESCRIPTION OF PREFERRED EMBODIMENT In the preferred embodiment, the film unit is a socalled integral negative-positive tripack employing dye developers as the dye image-providing materials and the positive component includes the aforementioned neutralizing layer in addition to the dyeable stratum.

As was heretofore mentioned, the present invention contemplates film units including a neutralizing layer for lowering the environmental pH, which layer comprises an acid salt of a polymeric base, i.e., the polymeric salt of a strong acid and a weak base which will hydrolyze to give an acid reaction. The neutralizing layers of this invention thus distinguish chemically as well as in the reaction product formed as a function of the neutralization from the acids heretofore employed for this purpose in that the salts of this invention form polymeric bases following neutralization, rather than salts. The respective reactions by which acids and salts effect neutralization may be illustrated as follows:

RCOOH NaOl-I RCOONa H O RNH 'HNO NaOI-I NaNO H O RNI-I The bases employed to form the salts of this invention generally are the amines, primary, secondary or tertiary, including aliphatic, aromatic or heterocyclic amines. As examples of useful amines of this description, mention may be made of polymers, copolymers and graft copolymers of Z-vinyl pyridine, 4-vinyl pyridine, 2-methyl-5-vinyl pyridine, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, N- vinylimidazole, t-butylaminoethyl methacrylate, aminoethylvinyl ether, etc. Also of interest are aminated polysaccharides such as deacetylated chitin, aminoethyl ether derivatives of cellulose, and the like.

The acids employed to form the salts generally have a pKa less than 4, preferably less than 3, and include the strong mineral acids such as nitric, hydrochloric, phosphoric and sulfuric, as well as strong organic acids such as lactic, chloroacetic, trifluoroacetic, p-toluene sulfonic, etc. Most preferred is nitric acid, since the nitrate salts are non-tacky and are not hygroscopic, as compared, for example, to the chlorides or sulfates.

The polymeric salts may be formed by reacting the amine monomer with the desired amount of acid and then polymerizing to form the polymeric salt; or by reacting the polyamine with the acid. Both reactions are 7 well known and per se comprise no part of this invention; and the salts obtained thereby are generally also old. In either 'of the above standard procedures for forming the salts, the amount of acid employed will depend upon the degree of neutralization or protonation desired. For example, if fully neutralized salts are contemplated, stoichiometric amounts of acid will be employed.

It will be appreciated that the amount or degree of neutralization of the salts will be at least in part dependent upon the degree of pH reduction contemplated in the particular film unit and system in which these salts areemployed. The lesser the amount of neutralization, the fewer the acidic ions which will be present for a given coverage of the salt. In a typical neutralizing layer, which is desirably thin and may contain on the order of 3000 mgsJft. or less of solids, the salt employed in this layer should preferably be at least SO'percent neutralized, i.e., atleast 50 percent of the basic groups should be neutralized, and most preferably at least 75 percent neutralized. However, salts having a lesser degree of neutralization may be completey adequate and hence'are also contemplated. In any event,

it will be appreciated that the absence of sufiicient acid ions at a given coverage of the salt may be compensated for by other means, including the use of higher coverages in the salt neutralizing layer. Accordingly, it is to be expressly understood that the polymeric salts of this invention include those bases which are not .fully neutralized or protonated.

*-;As examples of useful polymeric salts contemplated by this invention, mention, may be made of the followpoly-4-vinyl pyridinium lactate deacetylated chitin hydronitrate dimethylaminoethyl,methacrylate,hydronitrate graft copolymerof 4-vinyl pyridinium nitrate on polyvinyl alcohol, etc. -I'As wasv heretofore mentioned, the neutralizing layer of this invention is useful in systems wherein the photosensitive strataand the dyeable stratum are contained on separate elements; and in'systems wherein theyare contained together as a unitary film unit, e.g., in the integral negative-positive film units previously described. In the former type, the neutralizing layer is most preferably containediin association with the dyeable stratum,

e.g., in an image-receiving element comprising a support carrying, the neutralizing layer and the dyeable stratum, a spacer or timing layer preferably being disposedtherebetween. It may however be contained asa layer in the photosensitive element, i.e., in the element containing the photosensitive strata, as-is disclosed in U. S. Pat. No. 3,362,821. In like manner, in the integral negative-positive film units, the neutralizing layer is preferably associated with the dyeable stratum, e.g., on the side of the dyeable stratum opposed from the negative component, and most preferably a timing" layer is disposed between the layer and dyeable stratum.

As will be discussed in more detail hereinafter, the present invention is particularly useful in those film units, such as the heretofore described integral negative-positive film units, wherein'the negative and positive components are at least retained together following image formation as the final print. The invention will accordingly be illustrated by reference to a typical film unit of this description.

As shown in the drawing, such a film unit may comprise, as the essential layers, a layer 13 of cyan dye developer, red-sensitive silver halide emulsion layer 14,

interlayer 15, a layer of magenta dye developer 16,

green-sensitive silver halde emulsion layer 17, interlayer 18, yellow dye developer layer 19, blue-sensitive silver halide emulsion layer 20, auxiliary layer '21, image receiving layer or dyeable stratum 22, spacer layer 23, and a pI-I-reducing or neutralizing layer 24. Layers 13-21 comprise the negative component and layers 22-24 comprise the positive component. These essential layers are shown to be confinedbetween a dimensionally stable layer or support member 12 which is preferably opaque so as to permit development in the light and dimensionally stable layer 'or support member 25 which is effectively transparent to permit viewing of a color transfer image formed as a functionof develop ment in receiving layer or dyeable stratum 22.

Layers 12 and 25 are preferably dimensionally stable liquid-impermeable layers which when taken together may possess a processing composition solvent vapor permeably sufficient to effect, subsequent to substantial transfer image formation and prior to any substantial environmental'image degradation to which the resulting image may be prone, osmotic transpiration of processing composition solvent in a quantity effective to decrease the solvent from a first concentration at which the color-providing material is diffusible to a second concentration at which it is not. Although these ing in excess of about 3O,0 gms. of water/24 hrs/100 inF/miL, and may advantageously comprise a microporous polymeric film possessing a pore distribution which does not unduly interfere with the dimensional stability of the layers or, where required, the optical characteristics of suchlayers. As examples of useful materials of this nature, mention may be made of those having the aforementioned characteristics and which are derived from ethylene glycol terephthalic acid; vinyl chloride polymers;polyvinyl-acetate; cellulos'ede v rivatives, etc. As heretofore noted layer12 is of suffisensitive silver halide, e.g., silver chloride, bromide or neutralizing 1 cient opacity to prevent fogging from occurring-by light passing therethroug'h, and layer 26 is transparent to pennitphotoexposure and for viewing of a transfer image formed on receiving layer 23. f

The silver halide layers preferablycomprise photoiodide or mixed silver halides such as silver iodobromide or chloriodobromide dispersed in a suitable colloidal binder such as gelatin and such layers may typically be on the order of 0.6 to-6 microns in thickness.- It will be appreciated that the silver halidelayers may and in fact generally do contain other adjuncts, e.g., chemical sensitizers such as are disclosed inU. S. Pats. Nos. 1,574,944; l,623,4'99;: 2,410,689; 2,597,856; 2,597,915; 2,487,850; 2,518,698; 2,521,926; etc.; as

well as other "additives performing specific desired,

functions, e.g., coating aids, hardeners, viscosityincreasing agents, stabilizers, preservatives, ultraviolet absorbers and/or speed-increasing compounds. While the preferred binder for the silver halide is gelatin, others such as albumin, casein, zein, resins such as cellu- 9 lose derivatives, polyacrylamides, vinyl polymers, etc., may replace the gelatin in whole or in part.

The respective dye developers, which may be any of those heretofore known in the art and disclosed for example in U. S. Pat. No. 2,983,606, etc., are preferably dispersed in an aqueous alkaline permeable polymeric binder,,e.g., gelatin as a layer from about 1 to 7 microns in thickness.

lnterlayers 15, 18 and 21 may comprise an alkaline permeable polymeric material such as gelatin and may be on the order of from about 1 to microns in thickness. As examples of other materials for forming these interlayers, mention may be made of those disclosed in U. S. Pats. Nos. 3,421,892 and 3,575,701 and the copending applications of Richard J. Haberlin, Ser. No; 854,491, filed Sept. 2, 1969 now US Pat. No. 3,615,422, and Avtges et al., Ser. No. 119,331, filed Feb. 26, 1971, and now U. S. Pat. No. 3,625,685 etc. These interlayers may also contain additional reagents performing specific functions and the various ingredients necessary for development may also be contained initially in such layers in lieu of being present initially in the processing composition, in which event the desired developing composition is obtained by contacting such layers with the solvent for forming the processing composition, which solvent may include the other necessary ingredients dissolved therein.

The image-receiving layer may be on the order of 0.25 to 0.4 mil. in thickness. Typical materials heretofore employed for this layer include dyeable polymers such as nylon, e.g., Nmethoxymethyl polyhexamethylene adipamide; partially hydrolyzed polyvinyl acetate; polyvinyl alcohol with or without plasticizers; cellulose acetate with filler as, for example, onehalf cellulose acetate and one-half oleic acid; gelatin; polyvinyl alcohol or gelatin containing a dye mordant such as poly-4-vinylpyridine, etc. Such receiving layers may, if desired, contain suitable mordants, e.g., any of the conventional mordant materials for acid dyes such as those disclosed, for example, in the aforementioned U. S. Pat. No. 3,227,550; as well as other additives such as ultraviolet absorbers, pH-reducing substances, etc. It may also contain specific reagents performing desired functions, e.g., a development restrainer, as disclosed, for example, in U. S. Pat. No. 3,265,498.

The spacer or timing layer may be on the order of 0.1 to 0.7 mil. thick. Materials heretofore used for this purpose include polymers which exhibit inverse temperature-dependent permeability to alkali, e.g., as disclosed in U. S. Pat. No. 3,445,686. Materials previously employed for this layer include polyvinyl alcohol, cyanoethylated polyvinyl alcohol, hydroxypropyl polyvinyl alcohol, polyvinyl methyl ether, polyethylene oxide, polyvinyl oxazolidinone, hydroxypropyl methyl cellulose, partial acetals of polyvinyl alcohol such as partial polyvinyl butyral and partial polyvinyl propional, polyvinyl amides such as polyacrylamide, etc.

The neutralizing layer may be on the order of 0.3 to 1.5 mil. in thickness. in accordance with this invention, it will include one of the aforementioned salts, preferably one which is at least 75 percent neutralized, and the salt is most preferably contained at a coverage of less than 3000 mgs./ft.

The salts of this invention may be applied in accordance with knowncoating techniques to prepare the desired neutralizing layer, e.g., layer 24 of the illustrative film unit. It is most preferable to employ polymeric salts which are watersoluble and which may therefore be applied from aqueous coating solutions, thereby obviating the need for organic solvents and the obvious manufacturing disadvantages inherent in the use of organic coating solutions, e.g., the need for special equipment to handle these solvents which are typically volatile, including the storage thereof before use, and the involved danger in the use of such solvents. However, the coating disadvantages do not preclude the use of water-insoluble polymeric salts which need be coated from organic solutions, and from a photographic standpoint, these water-insoluble salts are equally applicable and are therefore contemplated by the present invention. Whether water-soluble or water-insoluble salts are employed, the reaction product, i.e., the polymeric base, formed by the pH reduction within the film unit is characterized as being hydrophobic. This hydrophobicity in turn provides certain distinct advantages over the use of prior hydrophilic acids in the neutralizing layer, e.g., the water-soluble polymeric acids described and claimed in the aforementioned Schlein et al application Ser. No. 165,171.

With the use of such hydrophilic acids, there is the inherent problem of water from the processing fluid piling up at the neutralizing layer and/or at the interface of the neutralizing layer and the timing layer. This piling up of water in turn causes certain distinct problems, chief of which is the tendency for delamination to occur, which separation renders the final print objectionable. While this problem is most pronounced in those film units wherein the negative and positive compo nents are retained together so that the processing fluid remains confined therebetween, e.g., in the heretofore described integral film units, it is also a problem, although to a lesser extent, in those systems wherein the respective negative and positive components are retained on separate elements which are separated following image formation.

From the foregoing discussion, it will be appreciated that the present invention permits one to apply the neutralizing layer as an aqueous coating, thereby obtaining all the advantages of aqueous coating systems during the manufacture of the film unit, while at the same time obtaining the advantages following development of hydrophobicity, due to the conversion of the polymeric salt from an initially hydrophilic material to a hydrophobic one.

The following examples show the preparation of illustrative polymeric salts contemplated by this invention.

EXAMPLE 1 Poly-4-vinyl pyridinium lactate was prepared by neutralizing 10.5 g. of poly-4-pyridine dispersed in water by adding 10.6 g. of 85 percent lactic acid.

EXAMPLE 2 To a dispersion of 16 g. of deacetylated chitin (prepared by acid hydrolyzing natural chitin) 9 g. of percent nitric acid was added to form deacetylated chitin hydronitrate.

EXAMPLE 3 .A solution of 31.4 g. of dimethylaminoethyl methacrylate was neutralized by adding 18 g. of nitric acid. The resulting mixture was polymerized by the addition of 0.062 g. of ammonium persulfate and 0.062 g. of sodium bisulfite to form poly-dimethylaminoethyl methacrylate hydronitrate.

EXAMPLE 4 Forty-fourg. of 4-vinyl pyridine were added to a deaerated solution of 11 g. of polyvinyl alcohol in 500 cc. of water under a blanket of nitrogen. After raising the temperature to 50C, the pH was adjusted to 1.5 with concentrated nitric acid and 6.6 g. of ceric ammonium nitrate was added. After several hours polymerization was complete, forming the graft copolymer of 4-vinyl pyridinium nitrate on polyvinyl alcohol.

In the foregoing illustrative Examples the polymeric salts were not isolated from the reaction mixture. Coating solutions for preparing the neutralizing layers of this invention may, if desired, by obtained from these reaction mixtures including the desired polymeric salt, or alternatively, if desired, the polymeric salt may first be isolated or recovered from the reaction mixture by standard procedures.

In any event, the neutralizing layers of this invention may be prepared by standard coating techniques employing polymeric salts such as those prepared in the foregoing illustrative Examples. By way of illustrating the types of film units to which this invention is directed, an integral negative-positive film unit of the type described and claimed in U. S. Pat. No. 3,415,644 and shown in the illustrative drawing may be prepared, for example, by coating, in succession, on a gelatin subbed, 4 mil. opaque polyethylene terephthalate film base, the following layers:

1. a layer of cyan dye developer dispersed in gelatin and coated at a coverage of about 100 mgs./ft. of dye and about 80 mgs./ft. of gelatin;

2. a red-sensitive gelatino silver iodobromide emulsion coated at a coverage of about 140 mgs/ft. of silver and about 70 mgs./ft. of gelatin;

3. a layer of a 60-30-4-6 copolymer of butylacrylate, diacetone acrylamide, styrene and methacrylic acid and polyacrylamide coated at a coverage of about 150 mgs./ft. of the copolymer and about 5 mgs./ft. of polyacrylamide;

4. a layer of magenta dye developer dispersed in gelatin and coated at a coverage of about 100 mgs./ft. of dye and about 100 mgs./ft. of gelatin;

5. a green-sensitive gelatino silver iodobromide emulsion coated at a coverage of about 100 mgs./ft. of silver and about 50 mgs./ft. of gelatin;

6. a layer containing the copolymer referred to above in layer 3 and polyacrylamide coated at a coverage of about 100 mgs./ft." of copolymer and about 12 mgs./ft. of polyacrylamide;

7. a layer of yellow dye developer dispersed in gelatin and coated at a coverage of about 70 mgs./ft. of dye and about56 mgs./ft. of gelatin;

8. a blue-sensitive gelatino silver iodobromide emulsion layer including the auxiliary developer 4'- met-hylphenyl hydroquinone coated at a coverage of about 120 mgs./ft. of silver, about 60 mgs./ft. of gelatin and about 30 mgs./ft. of auxiliary developer; and

9. a layer of gelatin coated at a coverage of about 50 mgs./ft. of gelatin.

The three dye developers employed above may be the following:

(I) W ll (IJH a magenta dye developer; and

a yellow dye developer.

Then a transparent 4 mil. polyethylene terephthalate film base may be coated, in succession, with the following illustrative layers:

l. a polymeric acid neutralizing layer containing poly-4-vinyl pyridinium lactate (as prepared in Example 1) at a coverage of about 2,000 mgs. /ft.

2. a graft copolymer of acrylamide and diacetone acrylamide on a polyvinyl alcohol backbone in a molar ratio of l:3.2:1 at a coverage of about 700 mgs./ft. to provide a polymeric spacer or timing layer; and

3. a 2:1 mixture, by weight, of polyvinyl alcohol and poly-4-vinylpyridine, at a coverage of about 400 13 mgs./ft. and including about 20 mgs/ft. of a development restrainer, l-phenyl-5-mercaptotetrazole, to pro vide a polymeric image-receiving layer containing development restrainer.

The two components may then be laminated together to provide the desired integral film unit.

A rupturable container comprising an outer layer of lead foil and an inner liner or layer of polyvinyl chloride retaining an aqueous alkaline processing solution may then be fixedly mounted on the leading edge of each of the laminates, by pressure-sensitive tapes, interconnecting the respective container and laminates so that, upon application of compressive pressure to the container to rupture the container's marginal seal, its contents may be distributed between the dyeable stratum (layer 3 of the positive component) and the gelatin layer (layer 9) of the negative component.

An illustrative processing composition to be employed in the rupturable container may comprise the following properties of ingredients:

Water 100 cc. Potassium hydroxide ll.2 gms. Hydroxyethyl cellulose (high viscosity) [commercially available from Hercules Powder Co., Wilmington, Delaware, under the trade name Natrasol 250] 3.4 gins. N-phenethyl-a-picolinium bromide 2.7 gms. Benzotriazole 1.15 gms. Titanium dioxide 50.0 grns.

2.08 gins.

i i l 1/ ll on i l u 0 y 0.5:? gins.

OH )Il l /)\y/ 74. w CMHU. i i i l! o O s 1.18 gms.

(E an,

This film unit may then be exposed in known manner to form a developable image and the thus exposed element may then be developed by applying compressive pressure to the rupturable container in order to distribute the aqueous alkaline processing composition. thereby forming a multicolor transfer image which is viewable through the transparent polyethylene terephthalate film base as a positive reflection print.

The following illustrates the preparation of another image-receiving element or positive component prepared in accordance with this invention. A solution of deacetylated chitin hydronitrate (as prepared in Example 2) was coated on a clear film base at a coverage of about 16 mgsJft. to provide a neutralizing layer. A graft copolymer of acrylamide and diacetone acrylamide on a polyvinyl alcohol backbone in a molar ratio of l:3.2:l was then coated at a coverage of about 800 mgs./ft." to provide a polymeric spacer or timing layer. Over this was then applied the image-receiving layer illustrated above as layer 3 of the positive component of the integral negative-positive film unit.

Similar film units may be prepared, for example, by applying the polymeric salt prepared in Example 3 at a coverage of about 2,400 mgs./ft. or the salt prepared in Example 4 at a coverage of about 2,300 mgsJft.

Since certain changes may be made in the above product and process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In a photographic product comprising a photosensitive element including at least one light-sensitive silver halide layer having a dye image-providing material associated therewith or an image-receiving element including a stratum adapted for receiving an image by diffusion transfer, said photographic product including a neutralizing layer for lowering the environmental pH subsequent to application of an aqueous alkaline processing compositon;

- the improvement wherein said neutralizing layer comprises a polymeric salt of a monomeric strong acid and a polymeric weak base.

2. A product as defined in claim 1 wherein said salt is the salt of an amine and an acid having a pKa less than 4. i

3. A photosensitive element including at least one light-sensitive silver halide layer having a dye imageproviding material associated therewith and a neutralizing layer comprising a polymeric salt of a strong acid and a weak base.

4. A photosensitive element as defined in claim 3 including a dyeable stratum adapted for forming a color image by diffusion transfer.

5. A photosensitive element as defined in claim 4 wherein said dyeable stratum is disposed between said silver halide strata and associated dye image-providing material and said neutralizing layer.

6. In an integral negative-positive film unit including a negative component comprising at least one lightsensitive silver halide emulsion layer having a dye image-providing material associated therewith, a positive component including at least a dyeable stratum, means for applying a reflecting layer between said positive and negative components in an amount sufficient upon development of said film unit to mask effectively said negative component and to provide a background for viewing a color image imparted to said dyeable stratum of said positive component by reflected light by applying an aqueous alkaline processing fluid to said film unit after exposure thereof, said film unit further including a neutralizing layer for lowering the environmental pH subsequent to application of said alkaline processing fluid;

the improvement wherein said neutralizing layer comprises a polymeric salt of a strong acid and a weak base.

7. A film unit as defined in claim 6 wherein said salt is the salt of an amine and an acid having a pKa less than 4.

8. A film unit as defined in claim 7 wherein said amine is a polymer, copolymer or graft copolymer of a member of the group consisting of 2-vinyl pyridine, 4- vinyl pyridine, Z-methyl-S-vinyl pyridine, dimethylamino-ethyl acrylate, dimethylaminoethyl methacrylate, N-vinylimidazole, t-butylaminoethyl methacrylate and aminoethylvinyl ether, aminated polysaccharides or aminoethyl ether derivatives of cellulose.

9. A film unit as defined in claim 7 wherein said acid is selected from the group consisting of nitric, hydrochloric, sulfuric, phosphoric, lactic, chloroacetic, trifluoroacetic and p-toluene sulfonic acids.

10. A film unit as defined in claim 6 wherein said 1 neutralizing layer is disposed on the side of said dyeable stratum opposed from said negative component.

11. A film unit as defined in claim 10 wherein a timing layer is disposed between said dyeable stratum and said neutralizing layer.

12. A film unit as defined in claim 10 wherein said negative component includes a red-sensitive silver halide emulsion having a cyan dye image-providing material associated therewith, a green-sensitive silver halide emulsion having a magenta dye image-providing material associated therewith and a blue-sensitive silver halide emulsion having a yellow dye image-providing material associated therewith.

13. A film unit as defined in claim 12 wherein said dye image-providing materials are initially soluble or diffusible in said aqueous alkaline processing fluid but are selectively rendered non-diffusible in an imagewise pattern as a function of development.

14. A film unit as defined in claim 6 including means for applying said aqueous alkaline processing fluid to develop said film unit.

15. A film unit as defined in claim 6 wherein said negative and positive components are confined between a pair of support members, at least the support member associated with the positive component being transparent.

16. A film unit as defined in claim 6 wherein said positive and negative components are confined on a transparent support member associated with said positive component.

17. A film unit as defined in claim 6 wherein said means for applying a reflecting layer comprises a layer of a white pigment disposed in a layer between said positive and negative components.

18. A film unit as defined in claim 6 wherein said means for applying a reflecting layer comprises a white pigment dispersed in said processing fluid.

19. A photosensitive element including a composite structure containing, as essential layers, in sequence, a dimensionally stable alkaline solution impermeable opaque layer, a layer containing a cyan dye developer, a red-sensitive gelatino silver halide emulsion layer, a layer containing a magenta dye developer, a greensensitive gelatino silver halide emulsion layer, a layer containing a yellow dye developer, a blue-sensitive gelatino silver halide emulsion layer, a dyeable stratum, a neutralizing layer comprising a polymeric salt of a strong acid and a weak base in an amount sufficient to effect reduction of a processing solution having a first pH at which said dye developers are soluble and diffusible to a second pH at which said dye developers are substantially insoluble and non-diffusible, a dimensionally stable alkaline solution impermeable transparent layer, means securing at least the side edges of said opposed layers in fixed relationship, and a rupturable container retaining an aqueous alkaline processing solution having said first pH and containing dispersed therein a white inorganic pigment in a quantity sufficient to mask effectively said silver halide layers and any dye developer associated therewith after development and to provide a background for viewing a diffusion transfer image formed by development of said film unit, by reflected light, through said transparent layer, said rupturable container being fixedly positioned and extending transverse a leading edge of said photosensitive element so as to be capable of effecting unidirectional discharge of the containers contents between said dyeable stratum and said third spacer layer upon application of compressive force to said container.

20. A film unit as defined in claim 19 wherein said cyan dye developer is a phthalocyanine dye developer; said magenta dye developer is a 1:1 chrome-complexed azo dye developer; and said yellow dye developer is a 1:1 chrome-complexed azomethine dye developer.

'21. A film unit as defined in claim 19 including a timing layer disposed between said dyeable stratum and said neutralizing layer.

22. A process for forming a visible image in color comprising the steps of exposing a photosensitive element as defined in claim 3 to form a developable image and thereafter applying an aqueous alkaline processing composition to said exposed element to form said color image.

23. A process for forming a color transfer image comprising the steps of exposing a film unit as defined in claim 6 to form a developable image and thereafter applying an aqueous alkaline processing composition to develop said image and to form, as a function of development, an imagewise distribution of dye imageproviding material which is transferred, at least in part, by diffusion, to said dyeable stratum to impart thereto a color transfer image viewable, without separation, by

reflected light as a positive color reflection print.

a t t i 

2. A product as defined in claim 1 wherein said salt is the salt of an amine and an acid having a pKa less than
 4. 3. A photosensitive element including at least one light-sensitive silver halide layer having a dye image-providing material associated therewith and a neutralizing layer comprisiNg a polymeric salt of a strong acid and a weak base.
 4. A photosensitive element as defined in claim 3 including a dyeable stratum adapted for forming a color image by diffusion transfer.
 5. A photosensitive element as defined in claim 4 wherein said dyeable stratum is disposed between said silver halide strata and associated dye image-providing material and said neutralizing layer.
 6. In an integral negative-positive film unit including a negative component comprising at least one light-sensitive silver halide emulsion layer having a dye image-providing material associated therewith, a positive component including at least a dyeable stratum, means for applying a reflecting layer between said positive and negative components in an amount sufficient upon development of said film unit to mask effectively said negative component and to provide a background for viewing a color image imparted to said dyeable stratum of said positive component by reflected light by applying an aqueous alkaline processing fluid to said film unit after exposure thereof, said film unit further including a neutralizing layer for lowering the environmental pH subsequent to application of said alkaline processing fluid; the improvement wherein said neutralizing layer comprises a polymeric salt of a strong acid and a weak base.
 7. A film unit as defined in claim 6 wherein said salt is the salt of an amine and an acid having a pKa less than
 4. 8. A film unit as defined in claim 7 wherein said amine is a polymer, copolymer or graft copolymer of a member of the group consisting of 2-vinyl pyridine, 4-vinyl pyridine, 2-methyl-5-vinyl pyridine, dimethylamino-ethyl acrylate, dimethylaminoethyl methacrylate, N-vinylimidazole, t-butylaminoethyl methacrylate and aminoethylvinyl ether, aminated polysaccharides or aminoethyl ether derivatives of cellulose.
 9. A film unit as defined in claim 7 wherein said acid is selected from the group consisting of nitric, hydrochloric, sulfuric, phosphoric, lactic, chloroacetic, trifluoroacetic and p-toluene sulfonic acids.
 10. A film unit as defined in claim 6 wherein said neutralizing layer is disposed on the side of said dyeable stratum opposed from said negative component.
 11. A film unit as defined in claim 10 wherein a timing layer is disposed between said dyeable stratum and said neutralizing layer.
 12. A film unit as defined in claim 10 wherein said negative component includes a red-sensitive silver halide emulsion having a cyan dye image-providing material associated therewith, a green-sensitive silver halide emulsion having a magenta dye image-providing material associated therewith and a blue-sensitive silver halide emulsion having a yellow dye image-providing material associated therewith.
 13. A film unit as defined in claim 12 wherein said dye image-providing materials are initially soluble or diffusible in said aqueous alkaline processing fluid but are selectively rendered non-diffusible in an imagewise pattern as a function of development.
 14. A film unit as defined in claim 6 including means for applying said aqueous alkaline processing fluid to develop said film unit.
 15. A film unit as defined in claim 6 wherein said negative and positive components are confined between a pair of support members, at least the support member associated with the positive component being transparent.
 16. A film unit as defined in claim 6 wherein said positive and negative components are confined on a transparent support member associated with said positive component.
 17. A film unit as defined in claim 6 wherein said means for applying a reflecting layer comprises a layer of a white pigment disposed in a layer between said positive and negative components.
 18. A film unit as defined in claim 6 wherein said means for applying a reflecting layer comprises a white pigment dispersed in said processing fluid.
 19. A photosensitive element including a composite structure containing, as essential layers, in sequEnce, a dimensionally stable alkaline solution impermeable opaque layer, a layer containing a cyan dye developer, a red-sensitive gelatino silver halide emulsion layer, a layer containing a magenta dye developer, a green-sensitive gelatino silver halide emulsion layer, a layer containing a yellow dye developer, a blue-sensitive gelatino silver halide emulsion layer, a dyeable stratum, a neutralizing layer comprising a polymeric salt of a strong acid and a weak base in an amount sufficient to effect reduction of a processing solution having a first pH at which said dye developers are soluble and diffusible to a second pH at which said dye developers are substantially insoluble and non-diffusible, a dimensionally stable alkaline solution impermeable transparent layer, means securing at least the side edges of said opposed layers in fixed relationship, and a rupturable container retaining an aqueous alkaline processing solution having said first pH and containing dispersed therein a white inorganic pigment in a quantity sufficient to mask effectively said silver halide layers and any dye developer associated therewith after development and to provide a background for viewing a diffusion transfer image formed by development of said film unit, by reflected light, through said transparent layer, said rupturable container being fixedly positioned and extending transverse a leading edge of said photosensitive element so as to be capable of effecting unidirectional discharge of the container''s contents between said dyeable stratum and said third spacer layer upon application of compressive force to said container.
 20. A film unit as defined in claim 19 wherein said cyan dye developer is a phthalocyanine dye developer; said magenta dye developer is a 1:1 chrome-complexed azo dye developer; and said yellow dye developer is a 1:1 chrome-complexed azomethine dye developer.
 21. A film unit as defined in claim 19 including a timing layer disposed between said dyeable stratum and said neutralizing layer.
 22. A process for forming a visible image in color comprising the steps of exposing a photosensitive element as defined in claim 3 to form a developable image and thereafter applying an aqueous alkaline processing composition to said exposed element to form said color image.
 23. A process for forming a color transfer image comprising the steps of exposing a film unit as defined in claim 6 to form a developable image and thereafter applying an aqueous alkaline processing composition to develop said image and to form, as a function of development, an imagewise distribution of dye image-providing material which is transferred, at least in part, by diffusion, to said dyeable stratum to impart thereto a color transfer image viewable, without separation, by reflected light as a positive color reflection print. 